Drilling apparatus for producing drilled holes having an undercut

Abstract

A drilling apparatus for producing undercut drilled holes and comprising a drill shaft including a bulge portion located between a stop ring mounted on the drill shaft and a drilling head mounted at the free end of the drill shaft, and which narrows towards opposite ends of the drill shaft.

I claim: 
     
       1. A drilling apparatus for producing drilled holes having an undercut, said apparatus comprising a drilling tool to be inserted into a drilling machine and including a drill shaft having a free end; a drilling head with a drilling plate located on said free end of said drill shaft; and a stop ring having a form of an annular disc and mounted on said drill shaft; said drill shaft having, in a region between said stop ring and said drilling head, a bulge portion, first and second portions extending from said bulge portion to said stop ring and said drilling head, respectively, and having a maximum diameter which is less than a maximum diameter of said bulge portion, at least one of said first and second portions having a tapered surface, and grooves for drilling dust extending through said stop ring. 
     
     
       2. A drilling apparatus according to claim 1, wherein said bulge portion has a cylindrical configuration. 
     
     
       3. A drilling apparatus according to claim 1, wherein said drill shaft has an annular groove, said apparatus further comprising a ring spring located in said annular groove and engaging said stop ring for retaining said stop ring. 
     
     
       4. A drilling apparatus according to claim 1, wherein said stop ring is rigidly mounted on said drill shaft, said drilling dust grooves ending in said stop ring. 
     
     
       5. A drilling apparatus according to claim 1, wherein said bulge portion has a central portion with a diameter which is less than the maximum diameter of said bulge portion, said appartus further comprising a bearing ring surrounding said drill shaft and mounted on said central portion of said bulge portion. 
     
     
       6. A drilling apparatus according to claim 5, wherein said bearing ring has a longitudinal slot. 
     
     
       7. A drilling apparatus according to claim 5, wherein said central portion has a lesser depth than said drilling grooves. 
     
     
       8. A drilling apparatus according to claim 1, wherein said drill shaft has a shank portion to be received in the drilling machine, and, in the region between said bulge portion and said shank, a convex collar over which said drilling dust grooves pass, and which has a side directed to said drilling head, said drilling apparatus further comprising a split sleeve engaging said side of said convex collar, serving as a centering sleeve and having a stop flange resting against said convex collar and defining said stop ring. 
     
     
       9. A drilling apparatus according to claim 8, wherein said drill shaft has a shaft shoulder spaced from said convex for retaining said split sleeve between said convex collar and said shaft shoulder. 
     
     
       10. A drilling apparatus according to claim 9, wherein said drill shaft tapers from said shaft shoulder towards said drilling head.